A post-mortem examination was carried out on Tuesday morning. The PSNI said in statement: "While we await the results of some tests, we do not at this stage believe Conall’s death was the result of a crime."

Chief Inspector Alan Hutton said: “We know that he was in the Metro Bar and left there and was seen on the city walls. From an extensive trawl of CCTV footage, we know that a number of people saw him and spoke to him. At one stage, Conall left the walls and went down into Foyle Street.

“The last confirmed sighting we currently have is of Conall returning to the walls via the steps near the library at about 2.45am on Sunday.

“Our renewed appeal is to anyone who was on the walls or in Foyle Street in the early hours of Sunday. If you saw him; if you spoke to him, please call the detectives at Strand Road station on the 101 non-emergency number.

“We are also investigating the possibility that sometime before his death, Conall’s wallet was stolen from him. No wallet was found in his possession, however, after extensive searches it was recovered by police.

“As part of our appeal, we would like to hear from anyone who was in the city centre generally on Sunday morning and knows or has heard of attempts to steal wallets from other people.”

A large part of the city centre was sealed off yesterday as police investigations into the death of 25-year-old Conall Kerrigan from Glack, south of Ballykelly, continued.

The area around Bank Place at the bottom of Shipquay Street and around the Millennium Forum was closed as forensics teams searched for clues.

Mr Kerrigan's family made an appeal for information over his whereabouts after he failed to return home as planned from a night out on Saturday.

His body was found the following night in the area of Bank Place at around 10.20pm, not far from where the last sighting of him was reported.

The dead man's cousin, Aaron Kerrigan, said he looked upon Conall as a brother.

"If you look at his photos, in every single one of them he's smiling," he added.

"That's what he epitomised. He could bring a smile to anybody's face just by a look or a word. He was somebody I looked up to. It's just really difficult."

There has been widespread shock in the small communities of Glack and Claudy following the death.

Conall, who was best man at his brother's wedding just three weeks ago, was a popular member of John Mitchel's GAA Club.

He had been living in England but returned home several months ago to set up his own plumbing business.

It is believed that he had been enjoying a night out in the city with his club team-mates when he went missing.

As a mark of respect, the club has cancelled all training and football matches for the remainder of the week.

John Mitchel's said in a statement that they had learned of the death "with a very heavy heart".

"Conall was a huge character, full of craic and a good friend to his peers," they said. "His passing hurts us all.

"There are just no words that will make sense of this, and everybody is struggling to come to terms with it.

"Our prayers and love go out to Conall, to his immediate and wider families, and to all of his friends."

Sinn Fein Councillor Paul Fleming expressed his condolences and said his prayers were with the bereaved family.

He added: "The entire community is in shock on hearing the terrible sad news.

"I wish to extend my sympathy and condolences to his family and friends at this time"